In the OP picture borrowed from another OP, I'd call the GB the easiest to look at and perhaps the easiest to use. The TC isn't as horrid as other comments have made it out to be, particularly when you take into account that the knobs are missing. I can understand that the lighted up panel can be a drawback in certain stage settings, but I think it would be very handy.
To me, the GK looks like a bad radio design without the channel readout.
I've come to respect JohnK's comments, but in this instance I've got to say that I never understood the VOX design. The only thing worse to me would have to be having the knobs on the back side of the head. I do agree though that the old Sunn design simply rocked when it came to ease of operation, to say nothing of pretty much rocking in general.
iJazz - I only wish I could suffer the "poor design" of the Genz.